Filling water tank

Hi,
When filling my new Motorhome via the whale attachment how do you no it's full? The manual says when full it will come out the overflow, which it did but very slowly. It was as though the tank came under pressure and slowed the flow down then forced the water out through the overflow underneath the van.
I also no you can look at the gauge in the van, but if you're one your own this is not possible unless you turned tap off first.
Long winded question I no but does this sound normal?

Hi,
When filling my new Motorhome via the whale attachment how do you no it's full? The manual says when full it will come out the overflow, which it did but very slowly. It was as though the tank came under pressure and slowed the flow down then forced the water out through the overflow underneath the van.
I also no you can look at the gauge in the van, but if you're one your own this is not possible unless you turned tap off first.
Long winded question I no but does this sound normal?

Another watering can man.
Filling up at home I rarely do, for the extra weight I like to avoid.
The gauge on my van really only shows 1/4, 1/2, 3/4 or full so not very accurate. I tend to drive with 1/2 full and fill up when I get somewhere. However in the winter and in France I may well try to keep the tank full, for frozen taps or taps turned off are common.